Researches are conducted on a multi-hop relay transmission technique which is an efficient data delivery scheme in an ad-hoc system. Recently, the multi-hop transmission scheme is attracting much attention as the technique to extend a service coverage of the cell at a low cost and to provide a high-speed data transmission to users in the wireless communication system. For example, the Institute of Electrical and Electronics Engineers (IEEE) 802.16j standard group is standardizing a Mobile Multihop Relay (MMR) technology.
A multihop transmission using a relay station (RS) in a wireless communication system is illustrated by referring to FIGS. 1, 2 and 3.
FIG. 1 depicts a conventional communication scenario between mobile stations (MSs) in the same RS service coverage in the wireless communication system. For communications, the MS 111 and the MS 112 in the same service coverage of the RS 110 operate in the wireless communication system as follows.
Provided that the MS 111 sends data to the MS 112, the first transmission 113 is made from the MS 111 to the RS 110 and the second transmission 114 is made from the RS 110 to a base station (BS) 100. The third transmission 115 is made from the BS 100 to the RS 110. Finally, the fourth transmission 116 is made from the RS 110 to the MS 112. For the data delivery from the MS 111 to the MS 112, radio resources are required for the data transmissions per interval (MS 111-RS 110, RS 110-BS 100, BS 100-RS 110, and RS 110-MS 112).
FIG. 2 depicts a conventional communication scenario between MSs in different RS service coverage within the same cell in a wireless communication system. The communications between the MSs in the same cell of the wireless communication system is performed as follows. Herein, the communication scenario between the MSs in the same cell considers that the MSs communicate via different RSs respectively within the same cell.
Provided that the MS 211 sends data to the MS 221, the MS 211 makes the first transmission 212 to an RS 210 and the RS 210 makes the second transmission 213 to a BS 200. Next, the BS 200 makes the third transmission 214 to an RS 220 and the RS 220 makes the fourth transmission 215 to the MS 221. As in FIG. 1, the data transmission from the MS 211 to the MS 221 requires radio resources per interval (MS 211-RS 210, RS 210-BS 200, BS 200-RS 220, and RS 220-MS 221).
FIG. 3 depicts a conventional communication scenario between MSs in neighbor cells of a wireless communication system. The communications between the MS 325 and the MS 341 in the neighbor cells of the wireless communication system is performed as follows.
An RS 320 belongs to a coverage of a BS 300, and an RS 340 belongs to a coverage of a BS 310. To transmit data from the MS 325 to the MS 341, the first transmission 321 is made from the MS 325 to the RS 320 and the second transmission 322 is made from the RS 320 to the BS 300. The BS 300 sends the data to the BS 310 over a backbone network. Next, the BS 310 makes the third transmission 323 to the RS 340 and the RS 340 makes the fourth transmission 324 to the MS 341. Hence, as in FIGS. 1 and 2, the data transmission from the MS 325 to the MS 341 requires radio resources per interval (MS 325-RS 320, RS 320-BS 300, BS 310-RS 340, and RS 340-MS 341) and a wired resource between the BS 300 and the BS 310 over the backbone network.
Utilization of the radio resource for the relay transmission is explained by referring to FIGS. 4 and 5 showing an Orthogonal Frequency Division Multiplexing (OFDM) frame structure.
FIG. 4 depicts a conventional half-duplex OFDM frame structure.
An uplink and a downlink in FIG. 4 are separated based on a transmission time. The DownLink (DL) transmission starts with one preamble symbol, a Frame Control Header (FCH), DL-MAP, UL-MAP, and data symbols in order. Receive/transmit Transition Gap (RTG) and Transmit/receive Transition Gap (TTG), which are guard times to distinguish UL and DL transmission times, are inserted between frames and between the downlink and the uplink at the end respectively.
The preamble symbol is used for network synchronization and cell search. The FCH symbol is used to carry frame constitution information. The DL MAP symbols include Information Element (IE) and constitution information of bursts transmitted in the downlink, and the UL MAP symbols include IE and constitution information of bursts transmitted in the uplink.
For the relay transmission, the frame can be divided into a BS frame 400 and an RS frame 410 based on subcarriers. In various implementations, the frame can be divided based on the transmission time. Herein, the BS frame 400 is subdivided into a DownLink (DL) subframe 401 and an UpLink (UL) subframe 402. The DL subframe 401 is subdivided into an access zone 403 and a relay zone 404. The access zone 403 is used to transmit data from the BS to the MS, and the relay zone 404 is used to transmit data from the BS to the RS. Likewise, the UL subframe 402 is subdivided into an access zone 405 and a relay zone 406. The access zone 405 is used to transmit data from the MS to the BS, and the relay zone 406 is used to receive data at the BS from the RS. The RS frame 410 is divided to a DL subframe 411 and a UL subframe 412. The DL subframe 411 is subdivided into an access zone 413 and a relay zone 414. The access zone 413 is used to transmit data from RS to the MS, and the relay zone 414 is used to receive data at the RS from the BS. Likewise, the UL subframe 412 is subdivided into an access zone 415 and a relay zone 416. The access zone 415 is used to transmit data from the MS to the RS, and the relay zone 416 is used to transmit data from RS to the BS.
For the relay transmission of FIGS. 1, 2 and 3, the first data transmission is performed to the access zone 415 of the UL subframe 412 through the UL MAP information of the DL subframe 411. The second data transmission is performed to the relay zone 406 of the UL subframe 402 through the relay UL MAP information of the DL subframe 401. The third data transmission is conducted to the relay zone 404 of the DL subframe 401 through the relay DL MAP information of the DL subframe 401. The fourth data transmission is conducted to the access zone 413 of the DL subframe 411 through the DL MAP information of the DL subframe 411.
FIG. 5 depicts a conventional full-duplex OFDM frame structure.
The preamble, the FCH, the DL MAP, and the UL MAP of the frame of FIG. 5 are substantially the same as in FIG. 4 and are thus not further explained.
For the full-duplex transmission, a BS frame 500 that is used to transmit data from the BS to the RS or the MS and data from the RS or the MS to the BS, a first RS frame 510 that is used to receive data from the BS to the RS and to receive data from the MS to the RS, and a second RS frame 520 that is used to transmit data from the RS to the MS and to transmit data from the RS to the BS are allocated to different frequency bands.
For the relay transmission of FIGS. 1, 2 and 3, the first data transmission is conducted into the access zone of the UL subframe 512 of the first RS frame 510. For the first data transmission, UL MAP information of the DL subframe 521 of the second RS frame 520 is used. Next, the second data transmission is performed into the relay zone of the UL subframe 522 of the second RS frame 520. For the second data transmission, UL MAP information of the DL subframe 501 of the BS frame 500 is used. The third data transmission is conducted into the relay/access zone of the DL subframe 502 of the BS frame 500. For the third data transmission, DL MAP information of the DL subframe 501 of the BS frame 500 is used. Next, the fourth data transmission is made into the access zone of the DL subframe 521 of the second RS frame 520. For the fourth data transmission, DL MAP information of the DL subframe 521 of the second RS frame 520 is used.
As discussed above, for the relay transmission in the wireless communication system based on the relay station, separate resources are allocated to the paths respectively. As a result, as the number of the relay hops increases, more resources are required.